A
newly discovered fish in the Mekong River in Vietnam has a, how shall
we say this, unique male anatomy: its penis is on its head.

And the weirdness doesn't stop there:

Male priapiumfish don't have a penis like humans and other mammals.
Instead they have a unique organ called a priapium, which faces backwards
and looks like a muscular nozzle. It's actually a modification of the
fish's pectoral and pelvic fins.

The priapium of P. cuulong has two attachments, both of which look
frankly dangerous. At the bottom near the tip, there is a forward-facing
serrated saw, or ctenactinium. Further forward, right under the head,
there is a forward-facing rod called the toxactinium.

No one has seen P. cuulong mating, but based on observations of
other species it's likely that the saw and rod are used for grasping
the female during mating. One goes on either side of her head, holding
her still while the male transfers his sperm.